Method of making thiosemicarbazide



United States latent O" r 1,751,456 r METHOD or MAKING rmosnwucannazmnGeorge E, Taylor,: Louis, assiguor to-Mo Delaware b b Nobrawmg;A'pplicatiou lnnuary 2%;1953,

Serial*No:"333, 840 a 1 (C11 tat-nest of" making. thiosemicarbaiide.

Thiosemicarb azide, r

transn ti al known and usefufchm'" a1 retire-mam factu're' ofvv'hiclimany method raves suggested and employed. However, for sneermorereasonsnot one ts been foundwholly satisfactory. All are expensive;many are inenic enrana time-e iigi, whileotners naminc'ultlyoperabieaasnazar some w th. as

rearrangement to thiosfemicarbazi'de below about 6.0. Among the moredesirable water-immiscible liquids successfully employed are oii'ssu'chas toluene; xylene, solvent na htha h t'aneg and kerosene. However; other inert Water-i cible o g em 1 yeclandthofse-havr boilingpoints theiange of f bout 100C. to about 220 C. are particularly fire-2,731,496 Patented Jan. 17, 1956 zine salt oianinorganic' acid (exceptnitric acid) with'a' wat'r s'blublethiocyahate salt, (2): remove thewaterfrom' thefresultant reaction mixture, thereby obtaining a cruderesiduecoiitaining hydrazine thiocyanate (NHzNHiHSCN). (3): slurry thecrude: residue so obtainedin a: water immiscible inertorganic-- liquid,and then ('4) heat-tho suspension so formed to rearrangethe hydrazinethio cyanate while maintaining the=pH- below about i 6.0 during therearrangement reactions I r Although excellent yieldsofthiosemicarbazide are-obtained when any water-soluble thiocyanate;salt reactive with a water-soluble neutralized -hydraz-ine salt ofanin.- organicacid'texcept nitric acid-)isemployed in accordance with--this'embodiment of the present invention the-preferred thiocyanatereactant is ammoniumthiocyanatet Higher yields; are obtainedwith-ammonium: thiocyanate than-when othenwater-soluble thiocyanates areemployed. In; fact; employing ammonium thiocyanate in. accordance withthisaspect ofthe present invention ingeneral, results inquantitative orsubstantially quantitative yields. Further, its usage results imessentially aone-stepprocess, 6: g., the handlin-glof waste solids duringthe course of the reactionis eliminated. Furthermore, the usageotamrnoniumthiocyanate insubstantially chemically equivalent amounts-asal reactantwith a hydrazine salt of an inorganic acid (except-nitricacid) in-an aqueous-medium generally results in an aqueous suspension-or solution of the reaction productspossessing a pH in the range of 5L0to 5.51 Upon subjecting. such an aqueous suspension or. solution to aw'ater remoyaloperatiom e; g. vacuum distillation; the hydrazinethiocyanate contained thcreinexhibi-ts little orno tendeincytodecompose. Furthermore, the hydrazine th iocyanate containing cruderesidue obtained upon removing the water fromtheyaforementionedsolution. or

suspension possessing a pH of 5.0 to 5.5 exhibits almost no tendency-todecompose when subjectedto heat during the subsequent rearrangementreaction The pl-foi this aforementioned hydrazine thiocyanate containingcrude residue taken at various tinies d'uring the rearrangement reactionremains constantly below 6.0. As aforenoted,

it is essential? that the pH dt th' hydrazine thio'c'yanzitec'ontainedis refluxed for about 2 hoursat' reducedpressure,

p the temperature during the refluxingbeing about 11541255 C; During therefluxing period the system is maintained at a pH in the range of about5.0 to about 6:0. The suspension is then cooled and filtered; The whitesandy filter cake so obtained is washed with several smallportions ofwater and then driedat 100 C. A quantitative thioseniicarbazideemploying as the starting material a a water-soluble neutralizedhydrazine salt of an inorganic acid except nitric acid. Theproceduralsteps of this embodimentm'ay be represented as follows: (1) react inair" aqueous medium a wate'f-sdluble he'litralized hydratainifig residue(that is the pH ofa'n aqueous'solutidn of the hydrazinetliiocyafiate'containing crude residue) during the rearrangement reaction possess a pHnot in excess of about 6.0, p

As'illiistjr'ativfepf this particular embodiment of this inverified isthe following:

Example II To a suitable reaction vessel equipped with a thermometr;stirrerand reflux condenser containing approximately 123 parts by weightof 98.5% pure NHQ-NHzuHzSOsand approximately 200 parts byweigh-t ofwater is added and intimately mixed approximately 125 parts by. weightof 28% ammonium hydroxide (aqueous solution) and approximately 78part-sby weight 0f 98.5 pure ammonium tliiocyanat'e; Upon filtering thefiltrate-iscfoundto possess apH of 51.5: The solution or filtrate soobtained is taken to dryness under vacuum. The crude residue is thenadmixed with approximately 385 partsby' weight of kerosene (div c.02770; B;- P. range L15 "-205 C.) and the suspension is refluxed atreduced pressure for 3- hours. The temperature at refiux is 120-122 C.During the refluxing period the system" maintained apH of approximately5.5. The suspension is thencoo-led and filtered. The white sandy filtercake so obtained is then; slurred in approximately 300 parts by weightof water and filtered'. Upon washing the filter cake with waterand'drying at C: ayield (approximately 83 parts by weight) in excess of 96%by weight oftheory of pure thiosemicarbaeideis obtained. I

due.

taining residue is slurried in approximately 1320 parts by a Otherwater-soluble thiocyanate reactants than the ammonium salt, e. g., thealkali metal thiocyanates, may be employed as starting materials inaccordance with the foregoing aspect of the process of this invention.In such instances it has been found advantageous to include a smallquantity of an ammonium salt of a strong acid (except nitric acid) e.g., ammonium sulfate, or an inr- 1 thereof. In prior methods,particularly those which employed the alkali metal thiocyanates asstarting materials, no control of pH was attempted. In view of thestrong acetate, potassium carbonate, or better still ammonium hydroxide,may be employed, the quantities employed being determined as thatrequired to raise the pH to a value below about 6.0.

As further illustrative of the process of this invention an aqueoussolution of hydrazine thiocyanate is prepared by, intimately mixing inapproximately 1500 parts by weight of water approximately 497.3 parts byweight of NH2NH2.H2SO4,- approximately 152.9 parts by weight of sodiumhydroxide, and approximately 309.7 parts by weight of ammoniumthiocyanate. The pH of the solution is adjusted to a value within therange of 5.0 to 5.5 by the addition of a small quantity of sodiumcarbonate, and thereafter the solution is taken to dryness under a -25mm. of mercury vacuum. The anhydrous crude residue so obtained isdivided into two equal parts, A and B, and each part is slurried intoluene. To suspension A alkaline nature of the alkali metalthiocyanates employed,

pH values in excess of the critical value, namely about 6.0, wereencountered. It is believed that it was as a result of such high pHconditions in the prior methods that the rearrangement reaction wasaccompanied by the evolution of large quantities of gaseousdecomposition liquid vehicles in the manner described, the formation ofdecomposition products is minimized to the point of negligibility andexcellent temperature control is effected.

As exemplary of another embodiment of this invention, the following isillustrative:

Example III To a suitable reaction vessel equipped with a thermometer,stirrer, and reflux condenser containing approximately 528 partsbyweight of 98.5% pure is added approximately 800 parts by weight ofwater. The hydrazine salt is neutralized by adding 160 parts by weightof sodium hydroxide dissolved in 400 parts by weight of water.Thereafter there is intimately mixed in the neutralized hydrazine saltsolution approximately 310 parts by weight of ammonium thiocyanate. Thecomplete aqueous solution so 'obtainedis adjusted to a pH of 5.0 by theaddition of a small amount of sodium carbonate. Vacuum is applied to thereaction mix and the water is distilled off leaving a substantiallyanhydrous crude resi- Thereupon the crude hydrazine thiocyanateconweight of kerosene ape. 0.770; B. P.-range 115 -205 C.) and thesystem is refluxed at reduced pressure for two hours at about 120-122 C.The crude residue exhibits a pH in the range of 5.0 to 5.5 throughoutthe refluxing operation. The suspension is then cooled and filtered. Thewhite sandy filter cake so obtained is then slurried in approximately1320 parts by weight of water and filtered. The filter cake is washedfree of residual sulfates and dried at 100 C. Approximately 292 parts byweight of thiosemicarbazide (an 80% yield based on hydrazine) isobtained.

While in the above example sodium carbonate was employed to adjust thepH it is to be understood that in instances wherein the system isconsidered too acidic that other salts of a strong base and a weak acid,e. g., sodium is added approximately 0.1 parts by weight of 50% sulfuricacid, while nothing is added to suspension B. Y The respectivesuspensions are then refluxed for one hour at 108 C. Upon cooling andfiltering the respective suspensions and isolating the desired productin each case, it is observed that while a high yield is obtained from Ba 6% higher yield is obtained from A. Excellent reaction control isobtained in each of the respective refluxing operations. I

a While in Example III caustic is employed to neutralize thehalf-neutralized hydrazine sulfate other materials may be employed suchas gaseous ammonia, ammonium hydroxide, potassium hydroxide, causticsoda, and the like. The aforementioned half neutralized hydrazinesulfate may also be neutralized with hydrazine hydrate.

When the alkali metal thiocyanates are employed'as reactants withneutral hydrazine sulfate (NHzNHa 2HaSO4 in accordance with thisinvention it has not been found necessary to remove the undissolvedsulfates during the course'of the reaction. Also inthose reactions whereammonium thiocyanate isemployed vas a reactant with NHzNHz.H2SO4neutralized with an alkali metal hydroxide it has been found unnecessaryto remove the undissolved sulfates. Although it is preferred to employconcentrated solutions of all of the reactants, dilute solutions are notobjectionable.

Although it is preferable to remove all the water present in thereaction mixture obtained by reacting a hydrazine salt of an inorganicacid (except nitric acid) with a water-soluble thiocyanate salt inaqueous medium during the vacuum distillation or other suitableevaporation operation so that the subsequently formed water-immiscibleinert organic liquid suspension be completely anhydrous it has beenfound expedient to obtain a substantially anhydrous hydrazinethiocyanate containing crude residue and remove the last traces of waterduring the refluxing or heating of the water-immiscible inert organicliquid suspension of the crude residue. Amounts of water up to one percent remaining in the crude residue subsequent to the waterremovaloperation present no serious problem. However, amounts of water retainedin the crude residue in'exc'ess of five per cent present a seriousproblemand materially effect the yield of thiosemi- 'carbazide.

The refluxing of the water-immiscible liquid suspension of the hydrazinethiocyanate in crude or pure state in the rearrangement reactionisordinarily carried out at temperatures above about C. and usually notover 130 C. While-the temperature employed will depend upon thereactionconditions, the refluxing operation is preferably carried out at-125 C. Although atmospheric pressure can be used it has been foundpreferable to employ reduced pressures.

While the present invention has been described in referenee toparticular embodiments, variations and modifications thereof may be madewhich are obvious to those skilled in the art without departing from thespirit or scope of the invention. For example, instead of hydrazinesulfate, neutralized or half-neutralized, the salts of hydrazine withsuch inorganic acids as hydrochloric acid, hydrobromic acid, phosphoricacid and the like, may be employed in preparing the intermediaryhydrazine thiocyanate.

This application is a continuation-in-part of my application Serial No.l86,667,filed September 25, 1950, now abandoned.

What is claimed is:

1. In the process for preparing thiosemicarbazide by the rearrangementof hydrazine thiocyanate, the step which comprises heating a suspensionof hydrazine thiocyanate in .a water-immiscible inert organic liquid toeffect rearrangement to thiosemicarbazide, the reaction system beingmaintained at a pH in the range of from about 5.0 to about 6.0.

2. In the process for preparing thiosemicarbazide by the rearrangementof hydrazine thiocyanate, the step which comprises refluxing asuspension of hydrazine thiocyanate in a water-immiscible inert organicliquid having a boiling point in the range of 100 C. to about 220 C. toefiect rearrangement to thiosemicarbazide, the reaction system beingmaintained at a pH in the range from about 5.0 to about 6.0.

3. In the process for preparing thiosemicarbazide by the rearrangementof hydrazine thiocyanate, the step which comprises refluxing underreduced pressure and at a temperature in the range of 100 C. to about130 C. a suspension of hydrazine thiocyanate and ammonium sulfate in awater-immiscible liquid hydrocarbon having a boiling point in the rangeof 100 C. to about 220 C. to effect rearrangement to thiosemicarbazide,the reaction system being maintained at a pH in the range from about 5.0to about 6.0.

4. The process of preparing thiosemicarbazide which comprises reactingin an aqueous medium hydrazine sulfate with ammonium thiocyanate insubstantially chemically equivalent proportions, evaporating the waterto provide a crude residue containing not more than 5% by weight water,admixing the crude residue so obtained with a water-immiscible inerthydrocarbon liquid having a boiling point in the range of 100 C. toabout 220 C., refluxing the suspension so obtained under reducedpressure and at a temperature in the range of 100 C. to about 130 C. toeffect rearrangement of the hydrazine thiocyanate to thiosemicarbazide,and recovering thiosemicarbazide, the pH of said crude residuethroughout the rearrangement reaction being maintained at a pH in therange of from about 5.0 to about 5.5.

5. The process of preparing thiosemicarbazide which comprises reactingin an aqueous medium hydrazine sulfate with ammonium thiocyanate insubstantially chemically equivalent proportions, evaporating the waterto provide a crude residue containing not more than 1% by weight water,admixing the crude residue so obtained with kerosene, refluxing thesuspension so obtained under reduced pressure and at a temperature inthe range of 115 C. to about 125 C. to eflect rearrangement of thehydrazine thiocyanate to thiosemicarbazide, and recoveringthiosemicarbazide, the pH of said crude residue throughout therearrangement reaction being maintained at a pH in the range of fromabout 5.0 to about 5.5.

6. The process of preparing thiosemicarbazide which comprises reactingin an aqueous medium hydrazine sulfate with ammonium thiocyanate insubstantially chemically equivalent proportions, evaporating the waterto provide a crude residue containing not more than 1% by weight water,admixing the crude residue so obtained with toluene, refluxing thesuspension so obtained under reduced pressure and at a temperature inthe range of C. to about 130 C. to efiect rearrangement of the hydrazinethiocyanate to thiosemicarbazide, and recovering thiosemicarbazide, thepH of said crude residue throughout the rearrangement reaction beingmaintained at a pH in the range of from about 5.0 to about 5.5.

7. The process of preparing thiosemicarbazide which comprises reactingin an aqueous medium hydrazine sulfate with ammonium thiocyanate insubstantially chemically equivalent proportions, evaporating the waterto provide a crude residue containing not more than 1% by weight water,admixing the crude residue so obtained with xylene, refluxing thesuspension so obtained under reduced pressure and at a temperature inthe range of C. to about C. to effect rearrangement of the hydrazinethiocyanate to thiosemicarbazide, and recovering thiosemicarbazide, thepH of said crude residue throughout the rearrangement reaction beingmaintained at a pH in the range of from about 5.0 to about 5.5.

References Cited in the file of this patent UNITED STATES PATENTS2,450,406 Bambas Oct. 5, 1948

1. IN THE PROCESS FOR PREPARING THIOSEMICARBAZIDE BY THE REARRANGEMENTOF HYDRAZINE THIOCYANATE, THE STEP WHICH COMPRISES HEATING A SUSPENSIONOF HYDRAZINE THIOCYANATE IN A WATER-IMMISCIBLE INERT ORGANIC LIQUID TOEFFECT REARRANGEMENT TO THIOSEMICARBAZIDE, THE REACTION SYSTEM BEINGMAINTAINED AT A PH IN THE RANGE OF FROM ABOUT 5.0 TO ABOUT 6.0.